Bottom Line:
We find lower concentrations and larger dimensions for both species of membrane-associated AβpE3-42 oligomers.Membrane-inserted AβpE3-42 oligomers were also found to modify the mechanical properties of the membrane.Taken together, our results suggest that membrane-inserted oligomers are the primary species responsible for membrane permeability.

Affiliation: Department of Bioengineering, University of California at San Diego , La Jolla, California 92093, United States.

ABSTRACTMembrane permeability to ions and small molecules is believed to be a critical step in the pathology of Alzheimer's disease (AD). Interactions of oligomers formed by amyloid-β (Aβ) peptides with the plasma cell membrane are believed to play a fundamental role in the processes leading to membrane permeability. Among the family of Aβs, pyroglutamate (pE)-modified Aβ peptides constitute the most abundant oligomeric species in the brains of AD patients. Although membrane permeability mechanisms have been studied for full-length Aβ1-40/42 peptides, these have not been sufficiently characterized for the more abundant AβpE3-42 fragment. Here we have compared the adsorbed and membrane-inserted oligomeric species of AβpE3-42 and Aβ1-42 peptides. We find lower concentrations and larger dimensions for both species of membrane-associated AβpE3-42 oligomers. The larger dimensions are attributed to the faster self-assembly kinetics of AβpE3-42, and the lower concentrations are attributed to weaker interactions with zwitterionic lipid headgroups. While adsorbed oligomers produced little or no significant membrane structural damage, increased membrane permeabilization to ionic species is understood in terms of enlarged membrane-inserted oligomers. Membrane-inserted AβpE3-42 oligomers were also found to modify the mechanical properties of the membrane. Taken together, our results suggest that membrane-inserted oligomers are the primary species responsible for membrane permeability.

fig2: AFM imagesof (A) AβpE3–42 and (B) Aβ1–42 aggregated peptides after different periods ofincubation. Images were acquired in air. A 10 μL droplet wasdeposited on a mica surface for 5 min, rinsed with ∼ 50 μLpure water and dried with gentle N2 flow. The verticalcolor-coded scale is 10 nm everywhere except for the 48 h images,where it is 50 nm.

Mentions:
AFM was used to characterize the morphology ofthe self-assembledspecies. Only globular and small linear oligomers were seen in theinitial state of the freshly prepared AβpE3–42 and Aβ1–42 oligomers (Figure 2). While annular AβpE3–42 protofibrilswere already seen after incubation for 30 min at room temperature(Figure 2A), globular Aβ1–42 oligomers were still found even after incubation for 14 h (Figure 2B). The diameters of AβpE3–42 oligomers changed significantly after 0.5 h, whereas the diametersof Aβ1–42 oligomers remained approximatelyconstant after 14 h (Table 1). The heightschanged by a factor of ∼2 for both peptides (Table 1). As regions with high concentrations of AβpE3–42 fibrils were already seen after 48 h (Figure 2A), only protofibrils and large quantities of Aβ1–42 oligomers were observed (Figure 2B). Aβ1–42 fibrils were found onlyafter incubation for several days. These results correlate well withthe ThT data discussed above (Figure 1A).

fig2: AFM imagesof (A) AβpE3–42 and (B) Aβ1–42 aggregated peptides after different periods ofincubation. Images were acquired in air. A 10 μL droplet wasdeposited on a mica surface for 5 min, rinsed with ∼ 50 μLpure water and dried with gentle N2 flow. The verticalcolor-coded scale is 10 nm everywhere except for the 48 h images,where it is 50 nm.

Mentions:
AFM was used to characterize the morphology ofthe self-assembledspecies. Only globular and small linear oligomers were seen in theinitial state of the freshly prepared AβpE3–42 and Aβ1–42 oligomers (Figure 2). While annular AβpE3–42 protofibrilswere already seen after incubation for 30 min at room temperature(Figure 2A), globular Aβ1–42 oligomers were still found even after incubation for 14 h (Figure 2B). The diameters of AβpE3–42 oligomers changed significantly after 0.5 h, whereas the diametersof Aβ1–42 oligomers remained approximatelyconstant after 14 h (Table 1). The heightschanged by a factor of ∼2 for both peptides (Table 1). As regions with high concentrations of AβpE3–42 fibrils were already seen after 48 h (Figure 2A), only protofibrils and large quantities of Aβ1–42 oligomers were observed (Figure 2B). Aβ1–42 fibrils were found onlyafter incubation for several days. These results correlate well withthe ThT data discussed above (Figure 1A).

Bottom Line:
We find lower concentrations and larger dimensions for both species of membrane-associated AβpE3-42 oligomers.Membrane-inserted AβpE3-42 oligomers were also found to modify the mechanical properties of the membrane.Taken together, our results suggest that membrane-inserted oligomers are the primary species responsible for membrane permeability.

Affiliation:
Department of Bioengineering, University of California at San Diego , La Jolla, California 92093, United States.

ABSTRACTMembrane permeability to ions and small molecules is believed to be a critical step in the pathology of Alzheimer's disease (AD). Interactions of oligomers formed by amyloid-β (Aβ) peptides with the plasma cell membrane are believed to play a fundamental role in the processes leading to membrane permeability. Among the family of Aβs, pyroglutamate (pE)-modified Aβ peptides constitute the most abundant oligomeric species in the brains of AD patients. Although membrane permeability mechanisms have been studied for full-length Aβ1-40/42 peptides, these have not been sufficiently characterized for the more abundant AβpE3-42 fragment. Here we have compared the adsorbed and membrane-inserted oligomeric species of AβpE3-42 and Aβ1-42 peptides. We find lower concentrations and larger dimensions for both species of membrane-associated AβpE3-42 oligomers. The larger dimensions are attributed to the faster self-assembly kinetics of AβpE3-42, and the lower concentrations are attributed to weaker interactions with zwitterionic lipid headgroups. While adsorbed oligomers produced little or no significant membrane structural damage, increased membrane permeabilization to ionic species is understood in terms of enlarged membrane-inserted oligomers. Membrane-inserted AβpE3-42 oligomers were also found to modify the mechanical properties of the membrane. Taken together, our results suggest that membrane-inserted oligomers are the primary species responsible for membrane permeability.